1. Field of the Invention
The present invention relates to an electrothermal furnace for an atomic absorption spectrometer for converting a sample to be analyzed into the atomic state, the furnace comprising a first hollow furnace part connected to a first pair of electrodes and including a first opening for introducing the sample, and a second hollow furnace part connected to a second pair of electrodes and including a second opening for introducing the sample.
2. Description of the Related Art
Such an electrothermal furnace is well known in the prior art. The advantages which are achieved in spectroscopic analyses with a two-part electrothermal furnace of the above-described type are illustrated in detail in the literature. A corresponding two-part furnace, also designated as a xe2x80x9ctwo-step furnacexe2x80x9d, consists of a graphite tube which is arranged directly above a graphite container receiving the sample. In the tube surface opposite to the container, there is provided an opening which is aligned with the position of the container and corresponds to the diameter thereof, the graphite tube and the container being however spaced apart from each other. The graphite tube and the container can be heated separately, the graphite tube being in general first heated to the desired high operating temperature and then the container with the sample. After vaporization the various components of the sample pass through the opening into the graphite tube by reason of the thermal movement of the atoms. The gap between the graphite tube and the container produces losses due to atoms exiting from the gap, whereby the efficiency of the analysis is impaired. To create reproducible analytical conditions, the positions of the graphite tube and the container are fixed mechanically. The relative position of the two furnace parts to one another is thereby defined. In such an arrangement the sample is passed by means of a suitable automatic device to the container via a dosing opening positioned at the accessible upper side of the graphite tube. Said dosing opening, however, reduces the sensitivity of the spectrometer because of diffusing sample atoms.
Furthermore, the alignment of the automatic device for the introduction of the sample is difficult. Furthermore, with the known exemplary electrothermal furnace, a spectroscopic analysis with an increased or reduced ambient pressure can only be carried out by way of a manual introduction of the sample using a bulky and complex vacuum or pump means.
It is the object of the present invention to improve the known electrothermal furnace with respect to the above-mentioned drawbacks.
Said object is achieved for an electrothermal furnace of the above-mentioned type by the measures that the first furnace part and the second furnace part are each mounted on holders that are movable between a first position and a second position such that in the first position the first furnace part can be fed with the sample and that in the second position the openings of the first and second furnace parts are aligned relative to each other such that the sample can be transferred from the first furnace part into the second furnace part, wherein a distance required for electrical and thermal decoupling between the first furnace part and the second furnace part is reproducibly defined.
With the inventive construction of the electrothermal furnace, the first furnace part can be fed with a sample such that the holders respectively receiving the first and second furnace parts are located in the second position. Thus, an additional dosing opening with the disadvantages entailed thereby, as is the case in the prior art, is not necessary. Furthermore, the second position of the holding means ensures that the mechanical fixation of the furnace parts is reproducible. Hence, there are reproducible analyzing conditions with respect to the light beam passing through the second furnace part and also with respect to the thermal transportation of the atomized sample components. A further advantage of the inventive electrothermal furnace is that the distance required for electrical and thermal decoupling can be minimized between the first and second furnace parts due to the exact and reproducible fixation of the holder in the second position, whereby the sensitivity of the spectrometer is improved in comparison with the prior art.
Advantageously, the holders are each made rotatable or pivotable or linear relative to one another or are made movable in any desired combination thereof, the holders being only movable along a defined connection path.
This has the advantage that the holders are movable relative to each other by easily producible elements, e.g. pivot joints or rails.
In a further embodiment of the invention, one of the holders is connected to a drive element for automatically transferring the first and second furnace parts into the first position and second position, respectively.
It is thus possible to automate the feeding operation while maintaining the mechanical accuracy, and thus to increase the number of the analyzed samples per unit of time.
Advantageously, the drive element comprises a pneumatic or electric drive unit. Hence, an atomization can be realized in a simple and inexpensive manner with a simple activation means which may be controlled by an operator or by a program.
In a further development, the first furnace part is arranged in a first recess in one of the holders and the second furnace part is arranged in a second recess in the other holder, the first and second recesses in the second position forming a combined cavity which is gas-tightly sealed to the surroundings.
This arrangement has the advantage that the first and second furnace parts can be acted upon with a reduced or elevated pressure, and that the sample can be analyzed under desired pressure conditions without requiring a bulky and complex vacuum or pump device.
Advantageously, the holders comprise a spacer which mechanically defines the second position. The necessary distance between the first and second furnace parts and the alignment of the first and second openings can thereby be designed easily.
In a further embodiment, the spacer comprises an elevated ring defining the first recess and including a seal on one of the holders, and a recess corresponding to the elevated ring with the seal and provided on the other holder.
Advantageously, the mechanical position of the two holders relative to one another and thus the position of the two openings are on the one hand ensured by the seal on the elevated ring in the radial direction, and the distance between the first and second furnace parts is fixed on the other hand while the seal simultaneously seals the first and second furnace parts in a gas-tight manner to the surroundings.
In a further embodiment, the spacer comprises a guide pin on one of the holders, and a guide bushing accurately matching the guide pin and provided on the other holder. The advantage of such an arrangement consists in the simple and inexpensive producibility of the spacer.
Advantageously, either the first or the second recess comprises at least one fluid supply opening. The sample to be analyzed can thus be subjected to an elevated or reduced pressure, and it is also possible to introduce additional gases, such as argon, into the first and/or second furnace part.
In a further advantageous design, the first pair of electrodes is connected in a gas-tight manner to one of the holders, and the second pair of electrodes to the other holder. This arrangement permits the use of discrete replaceable electrodes; a gas-tight seal of the first and second furnace parts to the surroundings is here possible at the same time.
Advantageously, the holders comprise a cooling element.